Hydraulic power transmission system

ABSTRACT

In a system comprising first and second drive units each including one or more hydraulic motors, a two-position valve is provided in circuit with the motors of one drive unit, the motors of the other drive unit being supplied independently of the valve; the valve has a first operative position for blocking flow of working fluid to the one drive unit and a second operative position for permitting flow of working fluid to the one drive unit, the valve being operable between its first and second positions for selective operation of one or both drive units.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a divisional of my copending application Ser.No. 305,453, filed Nov. 10, 1972, now U.S. Pat. No. 3,841,797, relatingto "Power Units".

BACKGROUND OF THE INVENTION

This invention relates to a hydraulic power transmission systemcomprising first and second drive units each including one or morehydraulic motors.

Hitherto, in such a system, no means has been provided to alter thetorque automatically and manually by cutting in and out the motorsselectively. In order to alter the torque it has invariably beennecessary to provide gears, clutches, brakes, etc., except in caseswhere a fluid flywheel was provided. A fluid flywheel has thedisadvantage of being inefficient at low speeds.

It is the object of the present invention to provide a hydraulic powertransmission system which overcomes the disadvantages mentioned, andwhich provides a particularly advantageous method of altering the torqueof a motor system comprising a plurality of motors driven from a commonhydraulic source.

SUMMARY OF THE INVENTION

According to the invention, in a system comprising first and seconddrive units each including one or more hydraulic motors, a two-positionvalve is provided in circuit with the motors of one drive unit, themotors of the other drive unit being supplied independently of thevalve; the valve has a first operative position for blocking flow ofworking fluid to the one drive unit and a second operative position forpermitting flow of working fluid to the one drive unit, the valve beingoperable between its first and second positions for selective operationof one or both drive units.

One embodiment of the invention, as applied to a power unit andtransmission system for a wheeled vehicle, will now be described by wayof example with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section taken through the axis of the powerunit;

FIG. 2 is a fragmentary top plan view of the power unit;

FIG. 3 is a section on line 3--3 in FIG. 1;

FIG. 4 is a section on line 4--4 in FIG. 1;

FIG. 5 is a section on line 5--5 in FIG. 1;

FIG. 6 is a section on line 6--6 in FIG. 1;

FIG. 7 is a section on line 7--7 in FIG. 1;

FIG. 8 is a section on line 8--8 in FIG. 6;

FIGS. 9, 10, 11, 12 and 13 show details of a plate valve assembly shownin FIGS. 1, 6 and 8;

FIG. 14 is an underneath plan view of the detail shown in section inFIG. 6, without the inlet valve assembly;

FIG. 15 is a diagrammatic drawing showing leakage control of oil fromthe pump pistons of the power unit;

FIG. 16 shows a section on line 16--16 in FIG. 1;

FIG. 17 shows a section on line 17--17 in FIG. 2;

FIG. 18 shows a central vertical section through the fuel injector ofthe unit, the section being on line 18--18 of FIG. 19;

FIG. 19 is a partly sectioned side elevation of the fuel injector;

FIG. 20 is a section on line 20--20 in FIG. 18;

FIG. 21 is an unsectioned end view of FIG. 18;

FIG. 22 shows the outside of a spool valve element;

FIG. 23 is a section on line 23--23 in FIG. 18;

FIG. 24 is a section on line 24--24 in FIG. 18;

FIG. 25 is a section on line 25--25 in FIG. 18;

FIG. 26 is a sectional view of a valve connector adapted to be used withthe fuel injector;

FIG. 27 is a part-sectional plan view of a control gear for starting andstopping the power unit;

FIG. 28 is a part elevation on line 28--28 in FIG. 27;

FIG. 29 is an unbroken plan view of the control gear;

FIG. 30 is an end elevation of the control gear viewed from the left inFIG. 27 with certain parts removed;

FIG. 31 is a sectional plan view on line 31--31 in FIG. 27;

FIG. 32 is a fragmentary view in the direction of arrow 32 in FIG. 27with certain parts removed;

FIG. 33 is a part elevation showing the end view of a solenoid;

FIG. 34 is a partly broken away side elevation of a reversible hydraulicmotor adapted for use with the power unit;

FIG. 35 is a section on line 35--35 in FIG. 34;

FIGS. 36 and 37 illustrate details of a planet gear bearing fromopposite sides thereof;

FIG. 38 is a section on line 38--38 in FIG. 37;

FIG. 39 is a section on line 39--39 in FIG. 34 with certain partsremoved, showing a planet gear without details of its teeth;

FIG. 40 is a schematic view of a gear wheel of the motor; and

FIG. 41, a combination of FIG. 41a and FIG. 41b, is a schematic overallrepresentation of the complete power unit and ancillary equipment;

FIG. 42 is a section on line 42--42 in FIG. 41;

FIG. 43 is a section on line 43--43 in FIG. 41.

THE POWER UNIT General

The power unit comprises an internal combustion engine having a pair ofopposed free pistons, a pair of pump units the pistons of which coactwith the engine pistons, a pair of constant displacement hydraulicaccumulators into which pressurized hydraulic fluid is pumped inaccordance with the expansion strokes of the engine pistons, inlet portsand exhaust ports under the control of the pistons for admittingcombustion air to, and exhausting combustion gases from, the engine, andvalve operated fuel injection means actuated in accordance with thecyclical movements of the pistons to control the injection of fuel intothe engine. The power output from the engine is a flow of pressurizedhydraulic fluid, which in the present example is delivered from a pairof smoothing accumulators and used to drive hydraulic motors.

Arrangement and Mechanical Construction

The mechanical construction of the power unit itself, and certaindetails of such construction, are illustrated in FIGS. 1 to 17, of whichFIG. 1 best illustrates the general arrangement of the unit. Referencewill now be made to these figures in particular.

At the heart of the power unit is a compression-ignition enginecomprising a single, water-cooled cylinder 101 having a ring of airinlet ports 102 and a ring of exhaust ports 103, and a pair of opposedfree pistons 104L and 104R of equal mass. The pistons 104L and 104R arefree to reciprocate within the cylinder 101, and the overall designincludes means to ensure that the pistons always move simultaneously inopposite directions and are also disposed symmetrically on oppositesides of a central position denoted by line 4--4 in FIG. 1. A fuelinjector 200 is bolted to the cylinder 101 at the central position, sothat its nozzle 201 is positioned to inject fuel into the space betweenthe opposed pistons at appropriate times, as will be describedhereinafter.

Each end of the cylinder 101 is bolted to a respective one of twosimilar hydraulic accumulator-pump assemblies 105, 106. The assembly 105(which will be described in detail, the assembly 106 being identical inconstruction) comprises a pump unit 107, a first, constant displacementhydraulic accumulator 108, and a second, high pressure or smoothinghydraulic accumulator 109, the assembly having a casing structureincluding a bulkhead 110 which is bolted to the cylinder and by bolts111.

The pump unit 107 provides an internal oil-filled space or pump chamber112, and houses a composite cylindrical or pump piston 113 which is areasonably leak-free sliding fit in the bulkhead 110. The combinedeffects of the momentum of the pump piston 113, and the pressure in thepump chamber 112, ensure that the pump piston 113 is always pressedagainst the engine piston 104L.

A groove 114 in the bulkhead allows oil leaking along the outer wall ofthe pump piston 113 to pass into a pipe 177 (FIG. 5) which conveys it toa float chamber 178. Within the float chamber 178 is a float 179, whichon rising uncovers a drain hole 180 leading back to a vented reservoir514, (FIG. 4) via a pipe X. A tube, 181 leading via a restrictor 182 toa hole 183 in the bulkhead 110 gives access to the air compression space117. A valve 184 may be used to open or close access to the aircompression space so that air may be extracted therefrom in order toform a vaccum with which to suck the pistons 104L and 104R into theirstarting position. The float 179 and drain hole 180 are preferably sodimensioned that the float will rise before its total submersion underany conditions of average pressure that may exist in float chamber 178.In any case after the engine is brought to rest, pressure in the floatchamber 178 will fall so that oil leaking along the outer wall of thepump piston 113 will flow into it, and when the level is sufficientlyhigh the float will rise and allow the leaking oil to flow down into avented reservoir 514 (FIG. 41).

The pump piston 113 is in the form of a hollow ram which defines aninternal oil space and contains a heavy plunger 115 which is free tomove back to a retaining screw 118, and forward to cover an oil flowrestrictor 116 at the inner end of the ram; it will move in this mannerunder the impetus of its own inertia, pressing against the oil flowrestrictor 116 at the inner end when the piston 104L is acceleratingduring the first part of its outward stroke and decelerating during thelast part of its re-compression stroke. The ram will be pressed againstthe retaining screw 118 during the last part of its expansion stroke andthe first part of its recompression stroke. The restrictor 116 allows acontrolled quantity of oil to pass into a hole shown by dotted lines 164and on through a number of holes 165 into a groove 166 round the piston104L for cylinder wall lubrication where the piston slides. A spring118A contained within the retaining screw 118 urges the solid rod 115inwards to close the restrictor 116 when the engine is at rest so thatoil cannot escape through the restrictor at this time.

The first, constant displacement accumulator 108 comprises a domedcasing providing a stepped cylindrical internal surface 120. The domedcasing houses a downwardly projecting cylindrical sleeve 121 in which apiston 122 is free to move axially up or down. The lower portion of saidstepped cylindrical surface constitutes a cylinder communicating withthe pump chamber 112 and locating a leak-free piston 123 which is freeto move axially up or down. The pistons 122 and 123 define within thefirst accumulator a space 124 of variable volume which contains nitrogenor other gas under pressure. A second, oil-filled space 125 is situatedabove piston 122, to or from which oil may be admitted or withdrawn viaa port 126 in the dome 127 of the casing. The piston 123 is formed witha flange 128 which is adapted to come to rest against a step 129 of saidstepped cylindrical surface 120 and to abut against the lower end of thesleeve 121, for limiting the downward and upward movements of the piston123. Thus the piston 123 is constrained to move between lower and upperlimit positions which determine the minimum and maximum charge levels ofthe accumulator, respectively. A sump 130 is formed by the piston 123,in which any oil that may leak into the space 124 will collect and fromwhich it may be withdrawn via a duct 131. This duct also serves forrecharging the gas space 124 and to adjust its pressure; a suitablevalve would normally be fitted into the duct 131.

It is necessary to ensure rapid establishment of inlet oil flow into thepump chamber 112 once the chamber pressure falls as the result of theflange 128 of accumulator piston 123 coming to rest against the step129, while the pump piston 113 still continues its outward stroke. Forthis purpose, an inlet oil assembly 132 is provided to control the flowof oil through a spring-loaded plate valve 133. In this assembly: (1)the mass of the moving element of the valve 133 is kept reasonably low;(2) a diaphragm 132D, backed by a suitable gas such as nitrogen,contained in a space 132G, keeps to a minimum the mass of oil that mustbe accelerated on each cycle; (3) the cross-sectional area of the oil,perpendicular to its direction of flow, is large so as to keep the oilvelocity low; (4) the inlet oil in space 132E is raised to a fairly highpressure, which for example might in a particular instance be 150 poundsper square inch. When the pump piston 113 moves inwards into the pumpchamber 112, the first accumulator is first charged to its full capacityand then oil is forced via a second automatic spring-loaded plate valve134 into the second hydraulic accumulator 109. The details ofconstruction of the second automatic plate valve 134, which isessentially a high speed one-way valve, are illustrated in FIGS. 9 to13. The first automatic plate valve may be similarly constructed. Asillustrated in FIGS. 9 to 13, the valve comprises essentially astationary valve element in the form of a grid, and a thin plate whichis formed as a complementary grid, the thin plate being urged intocontact with the stationary valve element by an array of contact withthe stationary valve element by an array of compression springs. Whenthe valve is closed, the grid elements of the thin plate close off thespaces between the elements of the stationary valve element; when thethin plate is displaced by a small amount, however, these spaces areopened simultaneously. Thus the valve opens substantially to its maximumextent with a minimal displacement of the movable element.

The second hydraulic accumulator 109, best shown in FIG. 6, is connectedto the oil delivery opening of the pump chamber 112, which opening iscontrolled by the automatic one-way valve 134. The accumulator 109comprises a domed casing housing a cylindrical sleeve 135 within which apiston 136 is free to slide axially up or down. The piston 136 defineswithin the sleeve 135 a space 137, which is filled with nitrogen orother suitable gas under pressure. A vent 138 (FIG. 17) for filling thespace 137 leads into the clearance space that exists between thecylindrical sleeve 135 and the casing 109. When the pump piston 113moves inwards it first charges the constant displacement recompressionaccumulator 108 by forcing the piston 123 up until the latter is broughtto rest against the lower end of the sleeve 121, and oil then passesfrom the chamber 112 via the one-way valve 134 into an oil space 139 ofthe second accumulator 109, which has an outlet port 140 from which thepressurized oil is supplied to the hydraulic load circuit.

Communicating with the air compression space 117 behind each of theengine pistons 104L and 104R is a thin spring-loaded air inlet valve 141fitted in an entrance 142, and a thin spring-loaded air delivery valve143 fitted in an outlet 144; these valves admit air into the compressionspaces 117 on the compression strokes of the pistons, and permit egressof air from the compression spaces on the expansion strokes of thepistons, respectively. The entrance 142 may be connected by flexiblemetal tubing to an air inlet filter, atmospheric air being filtered andadmitted through the valves. In the preferred embodiment illustrated inthe drawings, however, the entrances 142 are connected by a duct 145 tothe outlet of an air compressor 146. The duct 145 may also include anair cooler. The compressed air from the outlets 144, after cooling ifnecessary, is conveyed via ducts 147 (shown broken away in FIG. 1) to aninlet 148 communicating via an air inlet manifold 149 with the inletports 102 of the engine cylinder (see FIG. 3). The inlet ports 102 andthe ends of the air inlet manifold 149 are preferably shaped so as toinduce a swirling motion of the incoming air, for example as indicatedby the arrows of FIG. 3. In the present embodiment the depth of thechannel perpendicular to the cross sectional plane of FIG. 3, tapersfrom the inlet 148 to the ends of the manifold so as to promoteapproximately the same air velocity throughout the manifold. Thisproduces two elongated air flow vortices in the engine cylinder, asindicated in FIG. 3, Fuel is injected from the injection nozzle 201, asindicated in FIG. 4, at about maximum compression.

Additional openings 150 may be provided in the wall of the enginecylinder 101. These openings, one of which is presently shown closed bya cover 151, may be used to apply compressed air for moving the pistonsapart if necessary, (when the engine is inoperative,) or to connect apressure gauge for research or experimental purposes, or to provide analternative means for fuel injection to fuel injection timing, or toadmit air when the pistons are being set in a starting position, as willbe explained hereinafter.

The engine exhaust system comprises a casing 152 providing a storagespace 153, which communicates with the exhaust ports 103 via a manifoldor passage 154 in the engine cylinder. A casing 155 bolted to the bottomend of the casing 152 provides an internal space 156 which communicateswith the storage space 153 by way of ports 157. An intake tube 158connected to the upper end of the casing 155 projects upwards inalignment with the passage 154, the latter being spaced from the end ofthe intake tube. The casing 155 also provides an internal cylinderportion containing a spool valve 160, which is biased upwardly by aspring shown diagrammatically at 159. In operation of the engine, whenthe exhaust ports 103 are uncovered by the piston 104R towards the endof a compression stroke, the products of combustion enter the storagespace 153 and impinge upon the intake tube 158. If the kinetic energy ofthe exhaust gases is relatively low, the spool valve 160 remains at itsupper position and the exhaust gases pass to a silencer (not shown) viaducting 161. However, if the kinetic energy of the exhaust gases issufficiently high, the spool valve 160 is disposed downwards to coverthe ports 157; in this case the gases in the storage space 153, being ofincreased pressure, pass through a duct 162 to an exhaust turbine, thelatter being combined with the air compressor 146. The spent gases arefinally exhausted via a pipe 163 and a silencer (not shown).

Each of the engine pistons is formed with a circumferential annulargroove 169 having bevelled sides, into which a plunger 170 having acorrespondingly bevelled end may be forced. In order to lock the pistonsagainst movement when the engine is not running. In FIG. 1 the plungers170 are shown neither fully in nor fully out, but are shown forillustration in an intermediate position. Each plunger 170 is normallyheld out of the respective annular groove 169 when the engine isrunning, by a U spring 171 which engages a grooved portion 172 of theplunger. When required, the plungers 170 are pressed into theiroperative, piston-holding positions by actuating pistons 173; the latterare slidable in cylinders 174 and are actuated by hydraulic pressureapplied via oil connections 175 when the pistons 104L and 104R are nearthe ends of their expansion strokes. The plungers 170 hold the pistons104L and 104R approximately in the position shown in FIG. 1, against theforces exerted by the rams 113, the latter being urged by hydraulicpressure from the accumulators 108. The forward speed of each actuatingpiston 173 is controlled by an orifice in a plate valve 167; the partsare designed to permit comparatively free flow in the reverse directionwhen the engine is being started. A light spring 168 holds the valveplate normally forward.

The output of the engine is a flow of pressurized liquid. The amplitudeand frequency at which the engine pistons 104L and 104R reciprocate arevariable, depending upon the power that is being developed. Thepositions at which the pistons momentarily stop at the end of thecompression stroke are largely determined by the initial momentum of thepistons and the pressure of the initial cylinder air charge. Thepositions at which the pistons momentarily stop at the end of theexpansion stroke are determined by the momentum that they have gainedfrom the energy of combustion, the cyclic range of oil pressures, andthe rate of flow of the hydraulic liquid. To maintain an approximatelyconstant compression ratio in the engine cylinder 101, more energy willbe required at high intake air pressures than at low intake airpressures; however, the same invariable volume of oil, determined by thestroke of each piston 123 of the constant displacement hydraulicaccumulators, as it reciprocates between the limits of its movement,will always be set aside for the return strokes of the engine pistons.Therefore the average pressure of this oil must be altered as requiredin accordance with the pressure of the intake air. It can easily beshown that when the average oil pressure in each of the constantdisplacement accumulators 108 is low, (to accommodate low intake airpressure,) the average compression speeds of the pistons 104L and 104Rwill also be low and the time taken to effect the compression strokeswill be correspondingly long. Conversely, when the average oil pressurein each of the constant displacement accumulators 108 is high, thespeeds of the pistons 104L and 104R will be high, so that the time toeffect the compression strokes will be correspondingly short. The samefactors apply to the speeds of the pistons on the expansion strokes, sothat the time to complete the strokes will be an inverse function of theenergy developed. The net result is that the rate of reciprocation ofthe engine pistons will be low at low power outputs and high at highpower outputs.

POWER UNIT OPERATION

With the "stop" plungers 170 completely retracted, the engine pistons104L and 104R and the pump pistons 113 are initially in the positionsshown in FIG. 1 with the engine pistons moving towards one another; theengine pistons 104L and 104R and the pump pistons 113 together havesufficient momentum to give an air compression ratio of, say 20:1, orhigher. Subsequently to this initial stage the oil inlet plate valves133 open. The air inlet valves 141 are already open and the air deliveryvalves 143 are closed, so that air enters the air compression spaces inthe engine cylinder lying between the engine pistons and the bulkheads110. The pump pistons 113 also move out from the pump chambers 112,under the action of their momentum and the pressurized fluid passingthrough the inlet oil valves 133. At about the position when themomentum of the pump pistons, together with the momentum of the enginepistons 104L and 104R, is spent in compressing the air charge in thecylinder 101, fuel is injected into the cylinder by the fuel injector200; the gas charge temperature and the relative pressure then rises andthe engine pistons are caused to accelerate away from each other,performing their working or expansion stroke.

The one-way plate valves 133 then close and the pump pistons 113 areforced inwards by pistons 104, first to charge the accumulators 108,which are adjusted so as to yield at less pressure than the pistons 136of the variable displacement accumulators 109. When the pistons 123 havecompleted their strokes, which are terminated by the abutment of thesepistons against the lower ends of the sleeves 121, the pressure in thepump chambers 112 continues to rise and the one-way plate valves 134open against the pressure in the oil spaces 139 of the variabledisplacement accumulators 109. During normal running of the unit, thepistons 136 are at a higher position than that shown in the drawings,depending upon the pressure required. The surge of oil on each pumpingstroke, after first displacing the pistons 123 in the constantdisplacement accumulators 108, is absorbed in urging the pistons 136inwards against the pressure of gas in the gas spaces 137, but the oilis continually leaving at a more moderate velocity through the outletports 140. When the momentum of the engine pistons 104L and 104R isspent, the pistons stop and the high speed plate valves 134 close. Thepistons 123 are subjected to pressure from the gas above them and stillmaintain a substantial pressure on the oil in the pump chambers 112;this pump chamber pressure acts on the pump pistons 113 and acceleratesthe engine pistons 104L and 104R back along another compression strokeas already described. During the time in which the pistons 104L and 104Rare moving outwards on the expansion stroke, the pressure in the aircompression spaces 117 is increasing, and when this pressure exceeds thepressure above the air delivery valves 143, the latter open to admitthis air charge.

Outlets 176 from the pump chambers 112 are connected to pipes 515L, 515R(FIG. 41), as will be described hereinafter. A peripheral groove 119 isincorporated in the piston-rod bearing of each bulkhead as part of ameans to ensure synchronization of the engine pistons 104L and 104R, aswill also be explained hereinafter. By these means continuous running ofthe engine is achieved.

THE FUEL INJECTOR General

The fuel injector 200 of FIG. 1 comprises injection means for injectingpredetermined quantities of fuel into the engine cylinder, and actuatormeans for actuating the injection means in accordance with the airpressure within the engine cylinder so as to ensure that thepredetermined quantities of fuel are injected into the cylinder atappropriate times in relation to the combustion cycle of the engine.

The injection means comprises, basically, a fuel injection nozzle, avalve controlled supply chamber located behind the injection nozzle,means for admitting fuel to the fuel supply chamber, and a fuel pistonactuated by said actuator means to compress the fuel in the supplychamber and to expel the fuel therefrom to the engine cylinder via theinjection nozzle. The actuator means includes a spring-loaded shuttlevalve arranged to move towards one or other of two limit positions inaccordance with the gas pressure in the engine cylinder, and means forsupplying pressurized hydraulic fluid to actuate the fuel piston inaccordance with the position of the shuttle valve; the pressurizedhydraulic fluid is fed from a chamber housing a free piston which isurged in a direction to expel hydraulic fluid from the chamber,expulsion of fluid from the chamber being controlled by the shuttlevalve, which is arranged to cover and uncover a port leading to thechamber.

ARRANGEMENT AND MECHANICAL CONSTRUCTION

The fuel injector is illustrated in detail in FIGS. 18 to 26 of thedrawings, of which FIG. 18 best shows the interrelationship of itsworking parts. Reference will now be made to these figures inparticular.

In FIG. 18 is shown a portion of the engine cylinder 101, and portionsof the engine pistons 104L and 104R which define a combustion space S inthe engine cylinder into which fuel is injected by the fuel injector.The fuel injector itself is incorporated in a metal body 202, which ismachined to provide a number of internal passages and bores ashereinafter described, and which houses the essential elements of theinjection means and the actuator means referred to above.

The metal body 202 is formed with a stepped cylindrical bore 203, at theupper end of which is an assembly consisting of the injection nozzleitself 201, a spring-loaded valve 204 having a valve seat 205, a spacerring 206, and another spacer ring 205A which may be of relatively softmetal such as mild steel, those parts being clamped and retained inposition by an adaptor 207 which is screwed into the threaded upper endof the cylindrical bore 203. The adaptor 207 is located in a passage inthe wall of the engine cylinder 101, to which the fuel injector body 202is suitably connected, a sealing ring 208 being located so as to preventleakage of gases from the engine cylinder.

Located within the cylindrical bore 203 is a cylindrical barrel 209, thebarrel being a tight leak-free fit within the bore. A piston 210 havingtrunk extension 211 of slightly reduced diameter is slidably arrangedwithin the barrel 209 to define a space 212, constituting a fuel supplychamber, between the upper end of the trunk extension and the valve 204.A compression spring 213 encircling the trunk extension 211 biases thepiston 210 towards its lowermost position. Fuel is admitted to thesupply chamber 212 through a port 214 in the barrel 203, the portcommunicating with a supply inlet via a passage 215.

Also located within the cylindrical bore 203 is a second barrel 216,this also being a tight leak-free fit in the bore. The bottom end of thepiston 210 is castellated so that, as it is biased downwardly by thespring 213, a space 219 remains beneath the piston for the admission ofhydraulic fluid.

A piston valve 220, which is a low clearance running fit in the barrel216, is biased upwardly by a spring 221, the piston valve having aflange 222 against which the spring bears. Upward and downward movementsof the piston valve 220 are limited by engagement of the flange 222 witha step 223 in the barrel 216, and with a sleeve member 224,respectively. The piston valve 220 is provided for the purpose ofallowing rapid egress of used oil from the space 219 through an internalpassage 225 of the valve. The passage 225 communicates via radial holes226 with a shallow annular space 227 near the upper end of the valve.When the valve is in its upper position, the annular space 227communicates with the space 219 and permits oil egress, and when thevalve is in its lower position, the annular space 227 is isolated fromthe space 219. Thus the valve is closed in its lower position and openin its upper position.

The spring 221 is weaker, in terms of simple force, than the spring 213.However, in relation to the cross sectional areas of the piston valve220 and piston 210, respectively, against which the springs act, thespring 221 is the stronger of the two. When therefore the piston 210 ismoving outwards to expel the spent oil in space 219, the piston valve200 will be open; but when the castellated end of the piston 210 reachesthe inwardly extended end of the piston valve 220, the latter will cedeand close. Thereafter introduction of high pressure oil into the space219 will oppose the piston 210 and move it upwards, while simultaneouslyit will keep the piston valve 220 closed down.

In practice a very small leakage of oil from the space 219 is requiredwhen the piston valve 220 is closed, and for this purpose the upper endof the piston valve may contain a small longitudinal channel ofappropriate cross section.

Any leakage of oil into the annular space between the piston extension211 and the inner surface of the barrel 209 can pass out through a smallhole 228 and a one-way valve consisting of an O-ring 229 located in anannular groove in the outer surface of the barrel 209.

A screw threaded hole 231 in the metal body 202 communicating with thepassage 215 is adapted to receive a connector valve 232 (FIG. 26)whereby fuel is admitted to the passage 215 and thence to the supplychamber 212 via the port 214. The connector valve 232 comprises a valvebody having a first stem portion 233, which is adapted to be screwedinto the hole 231, a second stem portion to which a fuel supply line maybe connected, and a flange 234 which is adapted to bear against the fuelinjector body 202. Within the valve body is a valve member 235 biasedtowards its closed position by a spring 236.

The fuel injector body 202 is also formed with a second cylindrical bore237, housing a barrel 238 which is a tight stationary leak-free fitwithin the bore. Mounted within the barrel 238 is a spring-loadedshuttle valve 239, to which is connected a downwardly extending hollowrod 240. A carrier cup 242 is free to move axially to and fro in asleeve 248. A compression spring 241 contained within the carrier cup242 acts upon the rod 240 to urge the shuttle valve 239 to its uppermostposition, at which position the valve lies very close to, but is spacedfrom, the machined outer surface of the engine cylinder 101. The upperlimiting position of the shuttle valve 239 is determined by the abutmentof the carrier cup 242 against a flange 243 of a third barrel 244, thediameter of the flange 243 ensuring a tight leak-free fit in the fuelinjector body 202. A central hole 245 in the top of the carrier cup 242is aligned with the hollow rod 240 for receiving oil which leaks downthe rod, this oil passing via a port 246 to the drainage passage 218.Downward movement of the carrier cup 242 is limited by a step 247 on theinner surface of the sleeve 248.

Means are provided to ensure that the port 246 remains in line with thecorresponding hole in the fuel injector body 202, so that leakage oilmay pass freely to the passage 218. The flange 243 is kept firmly lockedagainst its seat in the body 202 by a screw 251, acting through thesleeve 248. A seal 299 is fitted round the top of the barrel 238 toprevent leakage of cylinder gas.

A passage 249 in the engine cylinder extends from the cylinder space `S`(FIG. 18) to the space immediately above the shuttle valve 239, so thatthe latter is exposed to cylinder gas pressure and will be caused tomove downwardly in the barrel 238 when the gas pressure exceeds a valuedetermined by the force exerted on the shuttle valve by the spring 241.The force exerted by the spring 241, and hence the value of cylinderpressure at which the shuttle valve is moved downwards, can bepre-adjusted by any suitable means, such as an adjustable screw plug250, located in the bottom end of the retaining screw 251.

The upper end of the barrel 244 is of reduced diameter so as to be atight leak-free fit in a recess machined into the lower end of thebarrel 238.

The working oil at suitable pressure is supplied to the fuel injector byway of a feed pipe (not shown) connected to an inlet adaptor 253including a spring-loaded one-way valve 254. The oil passes via apassage 255 to an annular space 256 surrounding the stem 257 of theshuttle valve 239, and thence through a passage 258 leading from thebarrel 238 into an oil space 259. The oil space 259 is defined by acylinder 260 which is a tight leak-free fit in a cylindrical bore closedat one end by a screw-threaded metal plug 262.

The cylinder 260 contains a close fitting free piston 263, from insidewhich protrudes a spring loaded detent, 265.

These parts are shown in greater detail in FIG. 25, from which it willbe seen that the detent 265 may slide back axially against the force ofa spring, 281, and that the detent contains an oil groove to enable itto move freely to and fro in the oil filled spaces.

When oil pressure is the same on each side of the piston 263, anotherspring 282 holds the piston fully forward so that the detent 265 ispressed against the barrel 238. The spring 281 is made stronger than thespring 282 to ensure that under these conditions the detent 265 will befully extended.

Behind the piston 263 is a space 266 of variable volume whichcommunicates through a spool valve 267 with a space 268. The bottom ofthe space 268 is closed by a screw-threaded plug 269, provided withfilling means 270. The plug 269 has an axially extending flange 271 towhich is cemented a deformable container 272 made from a highlyimpermeable material with high chemical and physical resistance to oil,such as the material sold under the trade mark "Teflon". The container272 is filled with a fluid of high compressibility, such as dimethylsiloxane, and is held at high pressure.

The admission of oil into the oil space 259 has the following result. Ifinitially the free piston 263 is at its innermost position, (to the leftas viewed in FIG. 18), then the piston is moved outwards by the flow ofoil, displacing oil from the space 266 into the space 268 and causingthe pressure in the container 272 to rise. The outward movement of thepiston 263 ceases when the pressure in the container 272 is equal to thepressure in the oil space 259. When the gas pressure in the enginecylinder 101 attains a certain value at which the shuttle valve 239 ismoved downwardly against the force of the spring 241, oil can no longerflow from annular space 256 down to passage 258, but when the shuttlevalve moves to its lower position oil can flow from the space 259 into apassage 273.

The initial pressure in the container 272 is controlled by the spoolvalve 267, details of which are shown in FIG. 23. The spool valve 267has an axially extending pressure equalizing bore 274, which allows freepassage of oil between spaces 275 and 276 at all times; this spool valveis shown separately in FIG. 22, from which it will be observed that thevalve is made from two bands of slightly reduced diameter 285, in orderto render its action less abrupt. The spool valve 267 is positionedbetween a first spring 277 and a second, rather stiffer, spring 278.Behind the spring 278 is a slidable regulating rod 279 fitted with anO-ring seal 280.

When the force on the regulating rod 279 is completely removed bywithdrawing an actuating rod 286 as far as it will go, then oil at highpressure from the passage 255 flows from the passage 283 via thecircumferential groove in the spool valve 267 into the space 268, andbrings it up to the same pressure as that existing in the passage 255;thus there will be no difference in oil pressure between the spaces 259and 266 to press the free piston 263 back when the shuttle valve 239rises to its uppermost position, as shown in FIG. 18. Under theseconditions the relatively strong spring 281, which lies inside the freepiston 263, pushes the detent 265 up to its shoulder and in so doingpushes the free piston 263 back a predetermined short distance againstthe force of the relatively weak spring 282. When the shuttle valve 239is next depressed, the free piston 263 moves forward under the higherpressure in space 266, against the combination of the pressure in space259 and the force on the detent 265. The free piston 263 is finallybrought to rest when it reaches the barrel 238 (or when flange 264reaches shoulder 261, if desired). This results in the oil contained inspace 259 being impelled through passages 258, 273, 294, and into thespace 219 to effect a limited stroke of the piston 210. Suitableproportioning of the extension of the detent 265 in relation to theposition where piston 263 is finally stopped will ensure the correctamount of fuel required by the engine for idling, stopping, or starting.This correct amount will be sufficient to ensure enough flow through thepump units 107 during prolonged idling to prevent a harmful temperaturerise.

A passage 287, (FIGS. 20 and 23) leads to the annular space 293 whichexists between the barrel 238 and the bore 237, which has a low averagepressure when compared with passage 255. When the spool valve 267 ispressed over to the left by means of the relatively strong spring 278compressing the relatively weak spring 277, the circumferential groovein the spool valve connects the space 268 with the passage 287, thusallowing some of the high pressure oil in the space 268 to escape and soto lower the pressure therein. This has the effect of allowing a greatermovement of the piston 263 before the pressures are equalized, so thatmore oil may be taken into the oil space 259.

A piston 288 (FIG. 23) sliding in a cylinder 289, which is bolted to thebody of the fuel injector, may rest against the spool valve 267. A sawcut across the face of the piston 288 where it abuts against the spoolvalve allows free passage of oil through the bore 274 when the spoolvalve is moved. Oil pressure is applied to the piston 288 through aninlet adaptor 290, and when this pressure is sufficiently high, thepiston 288 is able to override the spring 278 and thus prevent a fall ofpressure in the space 268, or even increase that pressure. The pressureacting against the piston 288 is affected by constrictions 291 and 292,as hereinafter described.

When the shuttle valve 239 is in its lower position, oil leaves thespace 259, impelled by the pressure within the deformable container 272acting through the free piston 263. The oil flows through the passage258 into an annular passage 293 within the bore 237. From the annularpassage 293 the oil flows through a passage 294 into the oil space 219beneath the bottom end of the piston 210.

The spring-loaded valve 204 of the nozzle assembly is of a reduceddiameter just below its seating portion, to provide an annular regioninto which fuel is fed along axial grooves in the outer surface of thevalve trunk. When this valve is opened by fuel pressure from below, itsstroke is limited by a pad 295. The spring of the valve ensures a rapidvalve return. Fuel flowing up through the valve passes through smallholes 296 in the fuel guide and pad 295 and finally out through thenozzle 201. The nozzle 201 and fuel guide 296 are designed together toabsorb as little compression energy as practicable from the fuel, as byway of viscous drag. They develop and retain maximum turbulence of thefuel, due to the 90° angular velocity change as the fuel passes acrossthe sharp edge orifice of the injection nozzle 201.

Fuel Injector-Operation

With the assembly in the condition illustrated, at the moment when it isrequired to initiate a fuel injection sequence, the spring 241 is urgingthe carrier cup 242 with a force corresponding to the engine cylinderpressure. In this condition, oil at high pressure, say 5000 pounds persquare inch, flows from the inlet adaptor 253 via passage 255 into theannular space 256, and thence into the oil space 259. The free piston263 is forced outwards, compressing the oil in space 268 and the fluidin container 272 to the same pressure. When in due course the enginecylinder pressure reaches a predetermined value, the shuttle valve 239is moved downwards to seal the annular space 256, and then to connectthe oil space 259 with the annular passage 293. Prior to this sequencethe piston 210 must have moved down and closed the piston valve 220;when the piston 210 is near the bottom of its stroke, the piston trunk211 uncovers the port 214, so that fuel will flow into the fuel supplychamber 212. The free piston 263, under the stored energy of thecompressed fluid in container 272, then expels oil from the oil space259, through the annular passage 293 and into the space 219, therebyforcing the piston 210 upwards. The port 214 is then closed by thepiston trunk 211, so that the fuel from the supply chamber 212 isexpelled past the spring-loaded valve 204 and through the nozzle 201.Fuel delivery ceases abruptly when the free piston 263 reaches the innerlimit of its stroke. During fuel delivery a small amount of the workingoil passes down the axial passage of the piston valve 220, through theslightly reduced diameter referred to earlier; this causes a sharp dropin oil pressure when oil flow from the oil space 259 ceases, which inturn causes a sharp cessation of fuel flow from chamber 212 and rapidclosure of the spring-loaded valve 204. With the reduction of oilpressure in the space 219, the piston valve 220, under the action of thespring 221, opens to allow oil in the space 219 to be rapidly expelledvia the drainage passage 218 back to a pressurized oil storagereservoir.

On the expansion stroke of the engine pistons, as soon as the enginecylinder pressure falls to a value less than that exerted by the spring241 on the shuttle valve 239, the latter returns to its upper positionand oil again flows into the oil space 259 in preparation for the nextinjection cycle.

As will be described later, means are provided to prime the space in theinjector, which space lies between delivery valve 204 and the outletorifice in 201. This is done immediately before the engine is started,in order to make up for any loss of fuel by evaporation which may haveoccurred. For this purpose a specific volume of fuel is forced throughthe fuel system with sufficient pressure to lift the non-return deliveryvalve 204, and then to re-fill the specified space.

CONTROL GEAR FOR STARTING AND STOPPING

The control gear for starting and stopping the power unit is illustratedin FIGS. 27 to 33 of the drawings, and will now be described withreference to these figures in particular.

The control gear comprises a metal body 300, to which are bolted a topcover plate 301, a side cover plate 302, and a spacer block 303. Anoperating rod 304 is mounted for forward and backward sliding movementin a guide space defined by the cover plates and spacer block. Atransmission rod 305, leading to the actuator rod 286 of FIG. 23, ispressed forward by the operating rod 304 when in the running position.

The metal body 300 houses a number of movable elements as shown,including a slide 306 arranged to move along an internal guide passage307 inclined at 45° to the faces of the metal body 300, two spool valves308 and 309, a pair of similar spring-loaded bolts 310, 311, and aspring-loaded detent 312. The body 300 is formed with a number ofinternal oil passages, providing a first inlet 313 by which moderate oilpressure is applied to the spool valves 308 and 309; an oil inlet 314connected to the outlet ports 176 of the power unit via connecting pipes515L, 515R; an inlet 315, connected to the delivery manifold 520 asshown in FIG. 41; an oil outlet 316 leading to oil connections 175(FIG. 1) to operate the plungers 170; an oil outlet 317 leading to avented reservoir; and an oil inlet 318 leading to the high pressure oilsource which actuates the fuel injector.

When the operating rod 304 is forward, the slide 306 is depressed andthe spool valve 308 is displaced from the position shown. A smallundercut 334 on the slide 306 prevents the spool valve 308 from turningwhen it is forward. When the operating rod 304 is in its rearwardposition, the engine is stopped. The drawing shows the operating rod inits rearward position to stop the engine, so that the slide 306 andspool valve 308 occupy the positions indicated and the shuttle valve 309has not yet responded to the "stop" signal.

When a force is applied by the operating rod 304, the spring-loadeddetent 312 resists the initial movement of the slide 306, so that enoughforce is built up against the operating rod to depress the detent andcause the spool valve 308 to be moved to its alternative position in onequick movement. The slide 306 is moved along the guide passage 307,depressing the spool valve 308 by engaging a wedge-shaped deflectingmember 319. When the slide has been displaced, there is no tendency forit to move, and the operating rod 304 can move freely until itencounters the transmission rod 305.

If there is sufficient pressure in the constant displacementaccumulators 108 to start the engine, forward movement of the operatingrod 304 is normally prevented by the spring-loaded bolts 310, 311, whichare urged by springs, such as 320, to the position shown in dotted linein FIG. 27. Out-of-balance forces on the bolts are counteracted byrollers 321.

A pair of rams, 322 and 323 act in opposition to the springs 320, andwhen sufficient oil pressure is applied to these rams, through an oilchamber 324 by oil from a high pressure accumulator 550 (FIG. 41) viainlet 318, and through an oil chamber 336 by oil from the pumping space107 via inlet 315, the bolts 310, 311 are retracted.

The spool valve 309 supplies oil to operate the stop plungers 170. Inthe condition shown in FIG. 27, the oil connections 175 (FIG. 1) areconnected to the low pressure reservoir via an annular groove 325 of theshuttle valve assembly through oil outlet 317. When the spool valve 309is moved to its upper position, high pressure oil from the inlet 318flows along a neck 326 of the spool valve 309 to the oil outlet 316, andthence to the oil connections 175 for actuating the plungers 170.

As shown in the drawing, the spool valve 308 is in its outermostposition and directs high pressure oil from inlet 318 through drilledholes 327 for actuating a ram 328. The spool valve 309 cannot move up,however, until it has been released by a bolt, 329; this bolt is engagedin undercut 332, under pressure from oil inlet 314 acting on piston 330.Pressure on the piston 330 can only be released during the compressionstroke of engine pistons 104 at about the instant when re-compressionaccumulator piston 123 (FIG. 1) is brought to rest, as its flange 128reaches the seat 129. At this point in the cycle of operations, thepressure in the pump chamber 112 is momentarily zero, and the platevalve 133 is starting to open. The time for the neck of spool valve 309to reach the annular groove 333 is determined by the apportionment ofthe diameters of the ram 328 and the orifice 331 in relation to thepressure acting on ram 328 and the cross sectional area of spool valve309. This time must be approximately equal to the time it takes for eachof pistons 104 (FIG. 1) to complete both what is left of its compressionstroke and most of its expansion stroke.

Pressure for controlling the bolt 329 is relayed from the right handpump chamber 112 through outlet 176R (FIGS. 1 and 41) and via connectingpipe 515, by means that will be explained hereinafter.

In this way, it is possible with correct apportioning of the dimensionsof the relative parts to ensure that the "stop" plungers 170 areadvanced when the engine pistons have the least possible momentum, soavoiding excessive shock.

THE HYDRAULIC MOTORS General

As previously mentioned, the output from the power unit is a flow ofhigh pressure oil. In the present embodiment the flow of oil is used todrive four dual-torque reversible hydraulic motors connected to drivethe four road wheels of the vehicle, respectively. The motors areequally adapted for forward and reverse driving, and each motor isadapted to serve as an active element of the vehicle braking system.

Each motor basically comprises a cylindrical casing forming a stator,and a geared rotor assembly comprising a sun gear which meshes with twopairs of planet gears, the sun gear being mounted on an output shaft towhich a vehicle wheel is connected, and the pairs of planet gears beingarranged respectively to receive high pressure oil from two inletmanifolds, whereby to drive the sun gear. The high pressure oil is ofcourse the oil delivered from the output of the power unit. Oil from thegear assembly passes to an outlet manifold having an outlet duct.Braking is effected by constricting the flow of oil from the outletmanifold.

Arrangement and Mechanical Construction

One such motor is illustrated in detail in FIGS. 34 to 40, and will nowbe described with reference to these figures in particular.

The motor comprises a main casing consisting of an inner wall member401, an outer wall member 402, and an enclosing ring 403 clamped betweenthe wall members. The main casing houses a sun gear 404 bounded on itsperiphery by the enclosing ring 403 and two pairs of planet gears 405,the planet gears being equally spaced around the sun gear. In FIG. 34 acut away portion 406 of end plate 430 and ring 418 reveals some of theintermeshing gear teeth. The encircling ring 403 is machined to providetwo pairs of diametrically opposed, crescentic lobe-shaped, cavities 407into which the planet gears fit exactly so as to be driven by incomingoil as hereinafter described.

The sun gear 404 is formed as a flange on a central main shaft 411,which is supported by two bearings 410 and 412, and at its front endcarries a stud bearing plate 409, which serves to carry the wheel of thevehicle (the studs not being shown). The bearing plate 409 is boltedonto a splined taper 413, held in place by a nut 414. (In FIG. 34, theparts 409 and 410 have been removed).

The three main casing sections of the motor are held together by bolts(not shown) which screw into tapped holes such as 415 through transverseholes 416. The tapped holes 415 would normally be in the outer wall 402,but for illustration purposes are diagrammatically represented as beingin the inner wall 401. The bolts pass through the encircling ring 403and also the inner wall member 401.

Two exactly fitting rings 417 and 418, with outer diameters exactlyequal to the outermost diameter of the sun gear 404, fit by means of amain inner diameter 419 on the shoulders seen on wall members 401 and402, and are sealed by means of "O" rings 420 and 421. They are lightlypressed inwards against the sun gear 404 and the planet gears 405, bytwo or more springs 422, and are prevented from turning by two or morestuds 423. A space 424 between the ring 417 and inner wall member 401,and a similar space between the ring 418 and outer wall member 402, arekept filled with oil under pressure from a pressurized space 425 viapassages 426; these passages for illustration purposes are not shown intheir true positions in FIG. 35, but are shown in their true positionsin FIGS. 37 and 38.

Each of the four planet gears 405 is rotatably journalled in bearingssuch as 427 and 428. These bearings are a tight sliding fit, and acomparatively leak-free fit, in a space bounded by the four cavities 407in the enclosing ring 403, and by the rings 417 and 418 and thecorresponding shoulders in the wall members 401 and 402. Each planetgear is bounded by two end plates 429 and 430, each of which is asimilar tight sliding fit in the bearings. These end plates separate thebearing and gear assembly from circular oil grooves 431 and 432, whichare located in the inner faces of the wall members 401 and 402, andmachined at a constant radius about the central axis of the motor. Thegroove 431 constitutes an inlet manifold, to which high pressure oil isfed through an inlet 431a from the oil delivery outlet of the powerunit; the groove 432 constitutes an outlet manifold from which oil isled away via a passage 432a and 432b. Drainage grooves may be placed atthe intersections of hole 432b and connected to grooves 449a. Each ofthe end plates 429 and 430 contains a small hole 433 which allows oil topass into the space 425 extending axially through the planet gear 405. Aspring 434 presses two valve plates 435 against the end plates 429 and430. Each of the valve plates 435 contains a bleed hole 436. Springs(not shown) are fitted into pockets 408, and serve to push the faces ofthe bearings 427 and 428 against the faces of the planet gears 405,similarly to the way in which the springs 422 push the end rings 417 and418 against the sun gear 404.

A further circular groove 437, constituting a second inlet manifoldhaving an inlet 437a, is cut into the inner wall member 401 and iscovered by the end plate 438, the latter being held by bolts (not shown)against the inner wall member 401.

One-way valves 439 and 440 are provided to allow oil to pass into thecircular groove 437 or 432 according to which is at the lower pressure.These valves are oriented at any convenient angle and are only shown intheir present position in the drawings for the purposes of illustration.

In this way a shallow circular depression 441 formed on each face of thesun gear 404 adjacent to a depression 442 in each of the wall members401 and 402, and interconnected by a hole 443, is permanently kept at arelatively low pressure and serves as a sink for leakage oil.

A circular groove 444 on the outer face of the inner wall member 401 andcovered by the end plate 438 is permanently connected to this lowpressure sink by an axially extending passage 445.

Circular grooves 446 and 447 are connected together as shown by apassage 448. Circular grooves 449 and 449a are interconnected in themanner shown by a network of passages 450, which continues through theinner wall member 401, and via a passage 451 into the low pressure area.The grooves 447 and 449 are interconnected by the bolt holes thattraverse them. The purpose of these grooves is to prevent any possiblespread, and increase, in the area exposed to high pressure oil, and thusto minimize stress on the bolts that hold the assembly together.

Oil passes between the circular manifold 432 and each of the planetgears 405 by means of four passages similar to the passage 432c. A slot452 is cut in the sealing ring 418, to allow the oil to pass through andenter the space between gears, as shown at 453, in FIG. 34. Oil passesbetween the circular inlet manifold 431 and one pair of opposite planetgears by similar means to those employed for the outlet manifold 432.The other pair of opposite planet gears are serviced by the circularinlet manifold 437 from two channels similar to 454, (which are likewisenot in the circular position shown in FIG. 35); oil then passes througha slot 455 cut through the periphery of the sealing ring 417.

Axial clearance between the inner faces of the bearings 427 and 428, andthe gears themselves, is minimized by oil pressure from the axial bore425. This pressurized oil traverses the planet gear, and acting on eachend of the bearing assembly, balances the pressure from the faces of thegears to keep bearings 427 and 428 snugly against them. This same oilpressure forces the end plates 429 and 430 outwards away from thebearings and thus seals all the circular grooves. Some of the oil flowsvia the passages 426 to perform a similar function against thesealing-rings 417 and 418. The pressure of oil in the hole 425 iscontrolled by the relative sizes of the inlet oil passage 433, fromwhichever of the oil manifolds is under pressure, and the oil-bleed 436in valve plate 435, to whichever of the manifolds is atused-oil-pressure. The inward force of the rings 417 and 418 may befurther adjusted by the radial positioning of the outer wall of thedepression 441.

When the motor is running under pressure, radial forces on the sun gear404 are all balanced out, but this is not necessarily so in the case ofthe four planet gears. In FIG. 40 the outside tooth diameter of a planetgear 405 is represented by a circle 456, and the root diameter isrepresented by a circle 457. The planet gear is entirely enclosed, inthe clockwise direction as shown in the figure, from the points 458 to459. The planet gear meshes with the sun gear 404, in which the outsidetooth diameter is represented by a line 460 and the root diameter by abroken line 461. Oil enters or leaves the assembly by the slot 452 inthe ring 418, and by a slot 463 (shown in dotted lines) situated on theother side of the planet gear in the ring 417. If the gear motor isbeing pressurized by oil through the slot 452, then it will be underpressure all the way round from the centre line 464, in a clockwisedirection to the point 459. This oil pressure will diminish according tothe amount of leakage between the gear and the main casing. Assumingthat there is no significant leakage of oil, then the whole planet gearwill be under full pressure, except for an area lying between the centreline 464, and the point 459; there will be a resultant force actingapproximately in the direction of the vector 465. To avoid the resultantimbalance of forces, two small depressions, such as 466, (indicatedonly, since the bearing in which they are machined is not shown in FIG.40) machined in one side of each bearing are filled with oil directlyfrom the inlet slot 452 in the sealing ring 418 and a correspondinglyblank hole 472 drilled into the sealing ring 417, which feeds a similardepression in the bearing that supports the other side of the planetgear, as shown at 39--39 in FIG. 34, and in FIG. 39. This exerts anearly opposite counterforce, vector 467, and the two will give rise toa much smaller net resultant, indicated by vector 468. In this mannerthe excessive out-of-balance forces on the bearings can be reduced to anacceptable level. When the torque of the motor is reversed, oppositepressures oppose the out-of-balance force in just the same way frompressure entrance 463 to depression 462.

Oil passages 469 and 470 for this purpose are indicated in dotted linesin FIGS. 34, 36, 37, 38 and 39. FIGS. 39 and 40 show that the oil may beled across the centre line 464 through the gears. The figures also showhow, for clockwise rotation of the planet gears, oil will be fed fromthe slot 452, which is at high pressure, and from the hole 472 to theoil pressure pads 466. For anti-clockwise rotation, the slot 452 will beat low pressure, and a similar slot 463 in the sealing ring 418 andcorresponding hole in the sealing ring 418 will be at high pressure, oilbeing fed through similar passages to pads 462. Oil enters on only oneside, since there is only one slot on each side of the sun gear forrunning purposes.

Hydraulic Motor Operation

In order to operate the motor for vehicular use at half the maximumtorque, high pressure oil is piped from the power unit to the inletmanifold 431, and comparatively low pressure oil is piped to the inletmanifold 437. The oil passes from the gear motor assembly into theoutlet manifold 432 and is piped back to the pressurized oil reservoir.For maximum torque, high pressure oil is piped to both of the inletmanifolds 431 and 437, in which case both pairs of planet gears aredriven, the used oil passing to the outlet manifold 432 and being pipedback to the pressurized oil reservoir as before.

In order to operate the motor in reverse, high pressure oil from thepower unit is piped into the manifold 432, which thus serves as theinlet manifold, and is returned to the pressurized reservoir via themanifolds 431 and 437, which thus serve as the outlet manifolds.

In order to apply a braking torque, the flow of oil from the outletmanifold, or manifolds, is restricted at some position in the outletsystem.

The motor may be modified to serve as a single torque reversible motorby omitting the manifold 437 and one pair of planet gears.

OVERALL SYSTEM Arrangement and Mechanical Construction

The general assembly of the preferred embodiment of the invention isillustrated diagrammatically in FIG. 41, and will now be described withreference to this figure in particular.

FIG. 41 shows the ancillary components of the overall system togetherwith the power unit 100, the fuel injector 200 mounted at a centralposition with respect to the power unit, the starting and stoppingcontrol gear 300, and four single torque reversible hydraulic motors400, the latter being arranged to receive the pressurized oil deliveredfrom the power unit and driven in a controlled manner as subsequentlydescribed. The motors 400 are substantially as hereinbefore describedbut in this case are adapted to operate on a single torque principle.One pair of motors is referenced 400L and the other pair is referenced400R.

A device 51 for automatically controlling the energy storage capacity ofthe first hydraulic accumulator sections 108, by controlling the gaspressure in the spaces 124 (FIG. 1), comprises a spool valve 501 backedby air at inlet pressure from a manifold 502 and assisted by a spring503. This spool valve is urged in opposition to its spring bias by apiston 504. The piston 504 is actuated by the oil pressure in a pipe506, which leads from a port 505, and to valves 66 and 67. A drainageport 507 leads via a pipe 508 back to a pressurized oil sump 68, whichwill be described hereinafter. Another port 510 allows oil to enter thedevice 51 from an output pressure manifold 511 of the power unit by apipe 512. Oil leaking from the spool valve passes out via a hole 513down to a vented reservoir 514. In the position shown, the force exertedby the piston 504 is greater than the combined force exerted by thespring 503 and the air inlet pressure, and so the spool valve is down,thus lowering the mean pressure of accumulator sections 108. However, ifthe intake air pressure at manifold 502 is raised, a point will bereached when it will drive the spool valve 501 up against the face ofthe piston 504 and allow the higher pressure oil from the outputmanifold 511 to pass from the port 510 to the port 505, at the same timecutting off loss of oil from the ports 505 and 507; mean pressure willthen rise in the constant displacement accumulators 108 until the piston504 is forced down when equilibrium is reached.

The purpose of the valve 67 is to keep the engine pistons 104L and 104Rin opposed synchronization. For this purpose two similar peripheralgrooves, 119 (FIG. 1) are situated, one at each end, in the bore inwhich each of the pump pistons 113 slides, and so placed as to beuncovered by the pump pistons 113 when the latter are nearly fullyforward. When the engine pistons are at about the innermost position,the one-way inlet valves 133 close, and there is a rapid pressure risein each of the pump chambers 112, and in each of the grooves 119.

If both the engine pistons are exactly in opposition, each of thegrooves 119 are exposed to the pump chambers 112 for the same length oftime. If however they are at all out of phase, for example if piston104L is ahead of piston 104R, then the groove 119L will be uncoveredsooner than the other groove, and will be closed to the pump chamber 112later.

The value of:

Pressure x Exposure Time

will then be greater in the one groove 119L than in the other groove. Itwill next be shown how this effect is used to continually correct anytendency for the engine pistons to depart from perfect opposedsynchronization.

Under these conditions oil from the first groove 119L (which isuncovered sooner) is led to an outlet and one-way valve 185L, FIG. 41;oil from the second groove 119R is led in the same way to a similarone-way valve 185R. Pipes lead from each of these one-way valves to adifferential or synchronizing valve 67.

The synchronizing valve 67 consists of a shuttle valve member 186,lightly held in the position shown, when at rest, by similar springs187. An oilway, 188, is always open to a neck 189 and is attached topipe 506. Two further oilways, 190L and 190R lead through pipes 191L and191R to the oil operated control spaces 125L and 125R in the constantdisplacement accumulators 108L and 108R. The shuttle valve member 186 ishollow and is always in communication with an oilway 192 which leads viapipe 193 back to the pressurized oil sump system. Two bleed holes 194Land 194R allow oil from the one-way valves 185L and 185R to leak intothe shuttle valve 186 and away through oilway 192. Since the pressuresurge, which occurs while the grooves 119 are exposed to the pumpchamber 112, cannot pass back through the one-way valves 185, it isstored to some extent in tubes 195L and 195R until it escapes throughthe bleed holes 194L and 194R. This effect may be increased if requiredby using comparatively large flexible tubing for each of the tubes 195Land 195R; alternatively an accumulator may be used.

When the engine pistons 104L and 104R are operating correctly in opposedsynchronization, the shuttle valve member 186 is in the position shownin FIG. 41, and so the pressure is practically the same in each of thepipes 191L and 191R and constant displacement accumulators 108L and108R. If, however, the piston 104L gains an advance over the piston104R, the value of:

Pressure x Exposure Time

will become greater for the former than for the latter pistons; theshuttle valve 186 will then be biassed towards the right. This willallow some of the control oil in space 125 (FIG. 1) to return to thepressurized sump system 639 (FIG. 41) by way of shuttle valve neck 196and oilway 192. Pressure in space 124 (FIG. 1) will then fall, so thatits mean effective pressure, and therefore the energy accumulated whilethe piston 123 is performing its compression stroke, will be less thanit was on the previous stroke. With less energy available to overcomecompression between engine pistons 104L and 104R, the inwarddisplacement distance of engine piston 104L will be reduced, with aconsequent reduction in the exposure time of the first groove 119L topressure in the pump chamber 107. This adjustment will continue untilboth engine pistons are effectively moving in synchronized opposition.

If instead, the piston 104R should draw ahead of the piston 104L thesame changes will occur in the opposite direction. In this case,however, when the shuttle valve member 186 moves to the left oil flowsinto the neck 197 and down into the value 186 and out through hole 198and oilway 192.

By these means the engine pistons are always kept in opposedsynchronization.

A pipe 515L is attached to the outlet 176L of the constant displacementaccumulator 108L of the power unit; a similar pipe 515R is attached tothe outlet 176R of the other constant displacement accumulator 108R. Oilfor charging the high pressure part of the machine is introduced throughtwo non-return valves 516L and 516R. The pressure in the pipes 515L,515R pulsates with the pressure in the hydraulic pump units 107 ofFIG. 1. Leading from one of these pipes, for example 515R, another pipe551 conveys oil to a pulsation and pressure control valve 57 (see FIG.41). This control valve serves three purposes: first it ensures that theengine can only stop when suitable conditions of minimum power andcorrect intake air pressure prevail; secondly it ensures a controlledpressure to operate a hydraulic oil pump motivated by medium pressureoil, the purpose of which will be described hereinafter; thirdly iteliminates high cyclic pressure differences in the tube 363 (FIG. 41)during normal running.

Valve 57 consists of a spool 356 which is urged downwards to theposition shown by a spring 357. When it is in the position, an oilway358 attached to the pipe 551 is given free access, by a neck 359, to anoil outlet 340. The oil outlet 340 leads to the entrance hole 314 ofFIG. 27, so as to control the bolt 329 as already explained inconnection with FIG. 27. The spool 356 contains a passage 360 which isconnected by a metering orifice 361 with the neck 359. Pressure at theoil outlet 340 acts through the metering orifice 361 and passage 360 toact on the lower surface of the spool 356 to oppose spring 357. Thedimensions of the spool 356 and spring 357 are so adjusted that when theengine is idling the average pressure transmitted from the pump units107 (FIG. 1) against the spool 356 produces insufficient force toovercome that exerted by spring 357; the spool 356 therefore stays inthe position shown in the drawings. However, when power from the engineis appreciably increased so that the average pressure in the pumpchambers 112 rises, it will overcome the force of the spring 357 and thelatter will cede; the spool 356 will then move up until it covers theoilway 358. As the pressure acting on the spool 356 is the same as thatexisting at the oil outlet 340, and the spool valve rises to block theoilway 358 whenever this pressure becomes sufficient to overcome theforce of the spring 357, the pressure at the oil outlet 340 can neversubstantially exceed the pressure exerted by spring 357, even though theaverage pressure of the pump chambers 112 may rise substantially. Thespool 356 may have a portion of slightly reduced diameter, as indicatedat 362, in order to increase its response time.

A pipe 518 is attached to the gas vents 138 (FIG. 17) of the smoothingaccumulators 109, to ensure identical pressures in their gas spaces 137.Gas can be inserted through a filler 519.

Output oil pipes 520 lead from the high pressure oil delivery outlets140 in the pumping units of the power unit and lead to the common pipe511, connected to a pressure control device 52. The purpose of thepressure control device 52 is to ensure that the delivery pressure intothe oil pipes 520 always exceeds the pressure of the accumulators 108.Without this, under conditions of very low pressure demand, oildelivered from the pump units of the power unit would pass straightthrough the plate valves 134 without energizing the constantdisplacement accumulators 108, and the engine would stop. The device 52consists of a piston valve 521, which is able to close onto a seat 522.The valve 521 is biased by a spring 523, and is loaded by oil at the oilcontrol pressure of the oil space 125 (FIG. 1) through a valve 66 (thepurpose of which will be described hereinafter) from pipe 506. It willbe seen that when pressure in the common pipe 511 appreciably exceedsthe combined pressure exerted by the spring 523 and oil from the space125, the piston valve 521 will open all the way and produce only a minorpressure drop oat this point. However, the pressure must be greater thanthe operating pressure of the constant displacement accumulators 108.

For the purpose of obtaining a low power output, for example to providethe power required to drive an average automobile around city streets orto cruise along a country road, an engine of the dimensions envisagedwould require only intake air at atmospheric pressure. Forhill-climbing, hard acceleration, or driving at high speed, the intakeair pressure should be boosted. Exhaust turbines and compressors thatwould be suitable for this purpose are well developed in the art, andwill not be dealt with in this specification. The device 146 of FIG. 1provides a method of controlling and using an exhaust turbine poweredcompressor. An alternative method is provided by the device 65 shown inFIG. 41. In this case gas from the exhaust ports, (shown covered by aheat resisting cover 525, to the right of the fuel injector 200) passesinto a pulsation attenuating space 526, and from there into an exhaustturbine 527, after which it is led out through an exhaust port 528, tobe taken to a silencer (not shown). A centrifugal clutch 529, isdesigned to operate when the ratio of fuel to air in the engine reachesa certain value, say 1 : 24, as evidenced by the exhaust turbineattaining a specified speed. When this specified speed is reached, thecentrifugal clutch 529 engages and a compressor 530 starts to revolve.Up to this time air has been coming in through the compressor entrance531, to pass freely through the compressor and leave via manifold 502.An air filler can be fitted to the compressor entrance 531. Six portssimilar to 532 on the power unit 100 admit air into the engine. Thepassages connecting these ports to the manifold 502 are not shown. Anair cooler (not shown) would preferably be included to lower the airtemperature after the air leaves the compressor 530. These would beconstructed according to established practice.

An electric generator 533 and a coolant pump are arranged to be drivenby the gas turbine shaft. Six further ports 534, three adjacent each endof the engine cylinder, delivers air through one-way delivery valvesafter compression by the engine pistons, and take it via a surgeattentuator and preferably an air cooler (neither of which is shown asthey also could be constructed according to standard practice) to theengine cylinder air inlet 148.

A control device 53 for preventing output oil pressure from rising abovethe desired maximum value, comprises a plunger 535, which is a lowclearance sliding fit inside a hydraulic spool valve 536, fed by outputoil through a pipe 537 from the output oil manifold 520. Normally thespool valve 536 is pressed against a shoulder on the left hand side, asshown in the drawing, by a spring 538. A pressure equalizing hole 539extending right through the spool valve 536 allows the latter to movefreely in each direction. A port 540, leads via a pipe 541 to the inletnozzle adaptor 290 of the fuel injector 200. A port 542 leads to a pipe543, which conveys oil back to the pressurized reservoir 68. The plunger535 and spring 538 are so dimensioned that when the output oil pressurein pipe 520, acting on the plunger 535, reaches the desired maximumpressure, the spool valve 536 moves back against the force exerted bythe spring 538 to uncover the oil port 540.

The power output of the engine is increased by applying pressure to theactuating rod 286 by means of an inverted L-shaped lever 544, whichcould be depressed by the actuating rod 305 under the influence of theoperating rod 304. The operating rod 304 could be advanced in the firstinstance by an accelerator pedal. Under certain conditions, as forexample when accelerating a vehicle very hard at a low speed, or whenclimbing a steep hill at perhaps two thirds of the top speed, it ispossible to raise the oil output pressure to above the designed limit,and thereby to develop more power than could be used at these speeds. Ifthis occurs, then as explained in the previous paragraph, the oil port540 is uncovered and oil flows at the limit pressure along the pipe 541and into the inlet adaptor 290 (FIG. 23). This oil acts on the piston288, as explained earlier in connection with FIG. 23, to press the spoolvalve 267 over to the right against the force of the spring 278, thusovercoming whatever force might be applied to accelerate the actuatingrod 286. Oil entering past the constriction 291 (FIG. 23) leaves via theconstriction 292, the relative areas of these two constrictions giving ameasure of control over the pressure acting on the piston 288. Thepressure drop due to passage of oil passing through the restriction 292,is the actual pressure acting on the piston 288. By these means it isimpossible to overload the system by running it above the designatedpressure. A safety system is incorporated by the addition of a port 542in the device 53; in case of any kind of actuating failure causing thepressure to rise above the required limit, then the spool 536 will movestill further back against the spring 538 and thus allow the oil toescape back to the pressurized reservoir 68.

The high pressure oil that is required to power the fuel injector isproduced by means of devices 54, 55 and 56. This same oil is used tooperate the "stop" plungers, 170 of FIG. 1, which are housed in casings545. The device 54 is a one-way valve designed with a very shortresponse time, so that it can take oil in during the brief pressuresurges that occur in the pump chambers 112 when the engine is idling. InFIG. 41, an element 55 represents a hydraulic accumulator providing acapacity which will store oil between surges. A high pressure pump 56motivated by medium pressure oil is provided. This pump will raise thepressure at this location to whatever is required by the fuel injector200, and the `Stop` plungers, 170 (FIG. 1). For example, 5000 pounds persquare inch could be required by the fuel injector, compared with anavailable 400 pounds per square inch delivery pressure in the feed pipe551.

The oil whose pressure is to be raised is taken from the ventedreservoir 514 and enters the constant pressure ratio high pressure pump56 by oilway 552. It is then delivered via oilway 554 to a high pressureaccumulator 550. The motivating oil enters by oilway 599 fromaccumulator 55 and valve 54; after its energy has been spent, it leavesby oilway 553 to return to the pressurized oil sump system 593 and 68.When sufficient pressure is available at the oilway 599, the pump 56will function automatically whenever thee outlet pressure falls belowthe required value.

The pressurized oil sump 68 must be able to contain all the oil that isexpelled from the accumulators 109 and 108 when they adjust from maximumto minimum pressure. The sump consists of a large hollow cylinder 555,in which a free piston 556 is able to move back and forth as dictated bydifferences in oil pressure acting on its top face 557 and its innerarea 558. The free piston 556 may ride on two seals 559. Oil is suppliedto the bore 600 of the free piston from a control valve 69 by a hollowstationary piston 601, sealed by a ring 602. Leaking oil is conveyedaway from vent 603 back to the vented reservoir 514.

The control valve 69 contains a shuttle 604 balanced between oil atpressurized oil sump pressure on one end 605 and a spring 606 at theother. When pressure in the sump line 593 exerts less force against theshuttle 604 than does the spring 606, the shuttle rests in the positionshown in the drawing.

Oil at the delivery pressure from the output manifold 520 enters thevalve 69 through an oilway 608 and (when the shuttle 604 is in theposition shown in the drawing) leaves by oilway 607. The areas 557 and558 are so proportioned that the output manifold delivery pressure, whenexerted against surface 558, is always greater than the pressure causedby spring 606 pressing against the shuttle 604. Therefore when, underworking conditions, the piston 556 and valve 604 are in the positionsshown, the piston 556 must be moving up. Conversely if the pressure inthe sump line 593, acting against the shuttle valve 604, gives rise to aforce appreciably greater than that exerted by the spring 606, the valvewill yield, at first closing oilway 607 and then opening it to thecylinder 509. Under these conditions the pressure exerted against thesurface 558 is identical with that exerted against the surface 557, andas the area of surface 557 is greater than the area of surface 558,piston 556 is impelled down.

Oil after leaving the valve 52 enters a manually operated valve 58 whosefunction is to reverse the direction of the oil. In the position shown,oil passes from a port 560 along the left hand neck of a valve spool 570and out via a port 561. After use, the oil returns via a port 562,passes along the right hand neck of the valve spool 570 and leaves itvia a port 563. If the valve spool 570 is pushed to the left, oil passesin via the port 560 and out via the port 562. Used oil then enters thevalve by the port 561 and leaves by the port 564. The ports 560 to 564completely encircle the cylinder so as to avoid the effects of radialpressure. A window 565 connected only to a return oilway 566 does notcompletely encircle the cyclinder, but occupies somehwat less than 180°of the cylinder periphery. Opposite the window 565 lies another window567 of equal dimensions, which is connected by an oil duct 568 to a mainworking pressure oilway 569. The purpose of the windows 565 and 567 isto prevent the valve spool 570 from being moved while the oilway 569 isunder pressure; the oil pressure acting through the high pressure window567 pushes the valve spool 570 against the low pressure window 565 andthus applies high frictional resistance to movement of the valve spool570. Further means are provided to prevent the valve spool 570 frombeing actuated if the vehicle is in motion, as will be describedhereinafter.

Each of the motors 400 is attached to a respective wheel of the vehicle.A valve 59 makes it possible to obtain traction with either two or fourwheels, and thus to double the traction force when required. When aspool valve 571 is in the position shown, oil passes from valve 58 downthrough the oilway 572, valve 59, oilway 573, to energize the two motors400L; at the same time oil passes through an oilway 574 to energize themotors 400R. Under these conditions all four motors are in traction. Thespool valve 571 is under the control of two forces: a spring 575 pushesit towards the left and a hydraulic ram 576 pushes it towards the right.When the spool valve 571 is over to the left, the connection betweenoilways 572 and 573 is severed and only the motors 400R are in traction.Under these conditions an automatic valve 578 leading from thepressurized reservoir 68, opens to keep oil flowing through the motors400L.

The selection of two or four wheel drive can be determined manually upto a certain vehicle speed, according to the desire of the operator, orit can be controlled automatically depending upon the resistance tomotion and the speed of the vehicle. In order to engage all four wheelsmanually, the operator momentarily energizes a double solenoid actuator,579. In order to revert to two wheel drive, he momentarily energizes theother half of the actuator 579. The first operation lifts a plungervalve 580 into the position shown, and thus allows high pressure oilfrom the oilway 574 to flow into an oilway 585; after passing through aspool valve 581, this oil acts upon the hydraulic ram 576, and pushesthe spool valve 571 over to the right. Actuation of the other solenoidpulls the plunger valve 580 down to its original position. Above acertain vehicle speed the pumping sections of the power unit are unableto generate sufficient oil pressure to maintain the vehicle in a fourwheel drive condition. For the purpose of reverting to two wheel drive,a flange 850F fits into a wide slot cut into one end of the spool valve581. Oil pressure acts upon the upper end of the spool valve 581 in thespace lying between its greater diameter and its lesser diameter, 581A,the whole area being exposed to pressure at the lower end. If,therefore, equal oil pressure is acting upon each end, the spool valve581 must rest in the upper position as shown. The lower end of the spoolvalve is exposed to oil taken from the low pressure point 582 of aventuri tube 583 through which the working oil passes. The reduced upperarea of the spool valve 581 is exposed to a high pressure point in thesame oilway. At low oil speeds the spool valve 581 rests in the positionshown, but when the oil speed is great enough, depending upon thedimensions of the parts concerned, the force acting on the lower part ofthe spool valve 581 becomes less than the force acting upon the upperpart of valve 581, so that the latter descends and takes the spool valve580 with it. Oil flow is then cut off from the space 589, (referred tosubsequently,); the spool valve 571 moves to the left to cut off theworking fluid supply to the motors 400L. A detent 584 is installed inthe assembly to ensure fast positive movement of the device.

Automatic determination of two or four wheel drive is effected by avalve 60. This consists of a two diameter plunger valve, the largerdiameter H-1 being a low clearance sliding fit in a barrel H-2, thesmaller diameter H-3 being a low clearance sliding fit in a barrel H-4.A peripheral duct H-5 allows oil to pass from a pipe H-6 to a pipe H-7when the valve is forced down. A spring H-8 normally holds the valve upand closed. If the resistance to motion exceeds a certain value,represented by an oil pressure near the maximum allowable, for instance2800 p.s.i., then this pressure forces the smaller diameter plunger H-3down against the force of the spring H-8; oil then flows into the pipe585, through the spool valve 581 and into a space 589. The oil acts onthe hydraulic ram 576 and forces the valve 571 to the right, therebydoubling the traction. This causes the oil pressure to fall to abouthalf its former value. The larger diameter of plunger H-1 is of such anarea that the spring H-8 is unable to close the valve, once opened,until the oil pressure due to resistance to motion falls to somewhatless than half the allowable maximum pressure, for example say 1000p.s.i. Thus, when the valve does close and the oil pressure thereforeimmediately doubles, this new pressure is sufficient to open the plungerH-3 immediately.

The outlet pipe H-7 passes through the venturi controlled spool valve581, as shown, so that it gives no access of oil to the chamber 589,until the speed of the vehicle is low enough for its oil volume demandto be capable of being satisfied by the pumps 107 of the power unit.

A device 61 is provided for arresting the vehicle's motion byrestricting the flow of used oil from the hydraulic motors. For thispurpose the braking command is applied to a rod E-1, which by forcing aspool valve E-2 up constricts the outflow of oil from the motors 400Land 400R as the oil passes between the oilways 566 and 593. A hole E-4connects the underside of the piston to the low pressure oilway 593.Upward displacement of the piston is limited by a projection, E-5. Aspring E-3, returns the spool valve E-2 to the position shown whenpressure on the rod E-1 is released.

When pressure rises in the oilway 594, it opens the valve 590, andenters the space 589 to force the ram 576 and valve spool 571 over tothe right to the position shown, thus ensuring braking effect on allfour wheels.

An orifice 591 in the ram 576 allows oil to flow from the oil space 589,but it is too small to reduce significantly the pressure therein whenoil is entering the chamber. A one-way valve 596, prevents oil fromleaving the space 589 through the oilway 597.

A hydraulic plunger E-8 consisting of a full diameter and a neck asshown, is open to the pipe 566 on the lower end. The plunger is normallyheld in the position shown by a spring E-9, supported in a free-fittingcup E-10. The force exerted by the spring E-9 against the plunger E-8 issuch that it is equal to the opposite force exerted by the oil on thissame plunger, at the maximum permitted pressure for the components.Above this pressure the plunger E-8 rises to uncover a circumferentialgroove E-11 and allow oil to pass into the space E-7. At the same timethe trunk of plunger E-8 covers an exit oilway E-12 to close escape ofoil from space E-7. As a result of this, pressure rises in the space E-7and, overriding the braking force applied to the rod E-1, forces theshuttle valve E-2 down; this reduces the flow restriction between theoilways 566 and 593, and thus prevents the braking oil pressure fromexceeding the maximum designed value.

A one-way valve, E-6, is inserted to allow oil into the passage 566whatever the position of the spool valve E-2. Because of this, oil isalways available if the brakes are locked on, as when the vehicle isstationary and on a hill, whether the manually operated valve 58 is inthe forward or the reverse position.

The control valve 66 (FIG. 41) is an automatic pressure operated valvewhose function is to ensure closure of the valve 52 in emergencybraking, if, for example, the brake pedal is depressed before theaccelerator pedal is released. It consists of a normally open spoolvalve 612 subjected on one side 613 to the braking oil pressure and onthe other side to the action of a spring 614. When the brakes areapplied, pressure rises in the spaces 566 and 613 to force the spoolvalve 612 over to the right against the action of the spring 614. Thisaction closes the oilway 615 and opens the oilway 616 to oilway 617 soas to admit the pressurized oil to the space 618 behind piston valve521. When the braking pressure in passages 616 and 617, combined withthe force of spring 523, exceeds the pressure in the output pressuremanifold 511, the piston valve 521 closes.

In order to ensure that the reverse valve 58 can only be operated whenthe vehicle is stationary, the operating rod 570R contains two gates:E-14, and E-15. These gates are also shown in FIG. 42. The brakeoperating rod E-1 also contains a gate, E-17 which is indicated bydotted lines in 61 and is also more clearly shown in FIG. 42 and FIG.43, the latter being a sectional elevation through 43--43 in FIG. 41. Itwill be seen that unless the brake rod E-1 is pressed all the way in, itis impossible to slide the reverse rod 570R in either direction; also itis impossible to push the brake rod E-1 all the way in until all motionhas ceased, because to do so would involve completely closing valve E-2.Any attempt to do this would raise the pressure in the space E-7sufficiently as to arrest the braking effort. A stiff spring mightusefully be interposed between the brake rod E-1 and the operating means(for example the brake pedal) in certain applications.

In reverse, pressure in the oilway 594 causes the valve 590 to open andso ensures that both sets of motors 400L and 400R are in traction.

If at any time the power output of the engine is drastically reducedwhile the vehicle is in motion, insufficient oil may flow from the pumpsof the power unit to keep the hydraulic motors full. To prevent this, aone-way valve 595 will open to keep the system full of oil.

As it is necessary when the engine is idling to keep some circulation ofoil through the main pump units 107 so that they will not accumulateexcessive frictional heat, means must be provided to dispose of this oilif the vehicle is stationary. For this purpose a pressure operated valve610 may be installed in the one-way valve 595; this would be designed toremain open until the oil reached a certain moderate pressure and toclose when this pressure was reached. The critical pressure at which thevalve closes is preferably significantly less than the `break-away`pressure required to set the vehicle in motion. The valve may consistsimply of a circular, slightly curved piece of spring steel, kept inplace when open, by the heads of four shoulder bolts 611. In practicethe one-way valve 595 and pressure operated valve 610 may be combinedinto a single element.

Valves 620, 622, and 623 are provided to release pressure when requiredfrom the entire hydraulic system. The valve 620 releases pressure in thesump and intake oil system; this consists of accumulator 68, oilways593, oil cooler 621, and inlet oil assemblies 132. The valve 622discharges pressurized oil from the operating oil manifold system 520and 511, into the pressurized oil sump system 53. The valve 623discharges the oil from the high pressure oil system back into thevented reservoir 514.

The system illustrated in FIG. 41 obtains high traction andcomparatively low speed operation with the four hydraulic motors 400Land 400R under power, and operates at half traction with only one pairof hydraulic motors 400L or 400R under power. If dual torque hydraulicmotors are employed, then all four motors may always be under power,each operating at maximum torque or half torque at any one time.

ELECTRICAL-HYDRAULIC SYSTEM

The control panel contains an ordinary starting key, and the engine canonly be started if this key is inserted and turned to the `on` position.When it is in the `on` position: (1) a normally closed solenoid-operatedfuel valve 624 opens to pass fuel; (2) a solenoid-operated lock 625normally extended into the accelerator-operated rod 304, when the latteris in its `stop` position, is withdrawn so that the rod can be advanced;(3) an electrical relay switch interposed between the motor of hydraulicpump 626 and pressure controlled switch 627 is closed (in the operatingposition), pump 626 then being automatically started by thepressure-controlled switch 627 (situated in the oil delivery manifold511) if the pressure falls below the value required for starting theengine, and being stopped by this same switch when the pressure reachesthe required value; and (4) a solenoid-operated valve 62 closes an oilpressure release passage 545 from the fuel injector 200 to the ventedreservoir 514 and then opens to allow oil flow to the fuel injector fromthe accumulator 550.

The pump 626 feeds through a one-way valve 629 to a pressure-operatedvalve 630 containing a spool 631. The spool has a neck 632 which isalways open to the oilway 633, and to spring chamber 634 by means ofdrillings 635 and (in dotted lines) 636. It also has another neck 637open to the oilway 638, which leads into the pressurized sump manifold639. Finally the spool contains another oilway 640 which leads tonon-return valves 516L and 516R.

If oil pressure in the hydraulic system is zero throughout, then whenthe aforementioned key is inserted and turned to the `on` position, theswitch 627 being closed, the pump 626 will immediately start.

At this time the spool 631 is in the position shown. Oil is then free topass through both oilways 638 and 640, but mostly through the oilway638. Pressure rises in the oil sump system 639 until the pressure issufficiently high to move the spool 631 over to the right against spring641. The oilway 638 is thus closed, so that all the oil flows into oilpipes 515L and 515R. Oil then flows into the pump chambers 112 (FIG. 1)past the delivery valves 134 and into the oil delivery passages 520 and511 (FIG. 41). The pressure continues to rise until it reaches the setvalue in the manifold 511, after which the switch 627 cuts out and thepump 626 stops.

OPERATION -- STARTING THE ENGINE

Normally when the engine is not running, the engine pistons are back alittle further than the position shown in FIG. 1 and the plungers 170are inserted further into the grooves 169. However, when the engine isfirst assembled the engine pistons might not be in the correct startingposition. In order to bring the engine pistons to their startingposition, the air compression spaces 117 are connected to a vacuum pump.This may be done through the valve 184 in FIG. 15. The discharge valves620, 622, and 623 are all opened, the air inlet entrance 531 beingblanked off; the vacuum pump is started, a cover, 151, or the fuelinjector, being removed.

The pistons move as soon as the vacuum is strong enough to overcome thefriction due to ring pressure and the piston weight. The vacuum pump isthen disconnected, the valves 620, 622, and 623 closed, and the inletair entrance 531 is opened up.

After this the starting key is inserted and turned in order topressurize the system in the manner already described. The pistons wouldactually be a little further back then they should be, with the plungers170 pressing against them, but when the pressure starts to rise in thepumping sections of the power unit the engine pistons move until theplungers 170 engage in the grooves 169.

The fuel injector should have been bench tested and left full of oil andfuel. The one-way valve 254 prevents loss of this oil. The one-way valve235 which screws into the fuel inlet of the fuel injector preventsescape of the fuel.

The accelerator pedal of the vehicle actuates the operating rod 304. Thespring-loaded bolts 310 and 311 make it impossible to advance the rod304 until the pressure in the accumulator 550 and constant displacementaccumulators 108 is sufficiently high as to ensure a good start. Once asufficient pressure is reached the rod 304 withdraws the bolts 310 and311. At this stage, when the rod 304 is pressed in a forward direction,it first of all encounters the resistance of the detent 312. When enoughforce has been build up to depress the detent, the slide 306 traversesrapidly, depressing the spool valve 308 in the process. This removes thepressure from the ram 328 and allows the spool valve 309 to move intothe position shown. The oil behind the plungers 170 is then able toleave via the outlets 316 and 317 and return to the vented reservoir514, of FIG. 41, so that the engine pistons 104L and 104R can push thelocking bolts 170 back. The engine pistons then accelerate rapidlytowards one another under pressure from the accumulators 108. At aboutmaximum compression, fuel is injected into the engine cylinder.

While the engine is standing idle, some loss of fuel will occur from thespaces included and adjacent to 296 (FIG. 18), which lie above thedelivery valve 204 enclosed by adaptor 207. This will be particularly soif the engine is hot and fuel with a low boiling point is being used. Asthis might lead to an insufficiency of fuel for re-starting, means areemployed to refill the nozzle automatically immediately before the firstinjection is made. These means are shown in FIG. 27 and will now bedescribed.

Fuel destined for the fuel injector first enters the hose fitting 350 toflow through the one-way valve 351 and into cylinder 349, from here itflows through an adaptor (not shown) in hole 352 (FIG. 29) which ismachined directly into the cylinder 349. From the hole 352 it isconveyed to the fuel inlet hole 231 via the one-way valve adaptor 232(FIG. 26).

A free piston 353 is acted on by the main delivery oil pressure frommanifold 520 via the oil entrance 315, and oppositely by the ram 354,which is urged forward when the engine is at rest by oil led from thehigh pressure oil supply 318. The dimensions are such that the forceexerted by oil pressure from the oil entrance 315 against the area ofpiston 353, is less than the force exerted by oil pressure from thesupply 318 acting against the end area of the ram 354. When, therefore,the spool valve 308 is in the position shown in FIG. 27, the passage 355is under high pressure and the ram 354 and piston 353 are also in theposition shown. The space 349 is, of course, always full of fuel.

When the spool valve 308 is pushed forward by the slide 306, in order tostart the engine, high pressure oil is cut off from passage 355. Thishigh pressure oil passes out through the space 346 and passages 327, andis returned to the pressurized tank via passage 358 and oil outlet 313.

As soon as the oil pressure in passage 355 falls, oil pressure from theoil entrance 315 urges the piston 353 forward so that the desiredquantity of fuel contained in space 349, which is unable to returnthrough one-way valve 351, is forced out through a pipe leading from theexit hole 352 to nozzle 232 (FIG. 26). This oil is forced on into thespace 212 (FIG. 18) above the trunk extension 211, and past the deliveryvalve 204, to refill the spaces enclosed by adaptor 207, in advance ofthe actual injection stroke. A small quantity of fuel inevitably passesthrough the nozzle into the engine cylinder at this time, and is wasted.This however will not hurt the engine, and it will take about fifteenthousand such starts to consume a gallon of fuel. The volume of fuelinjected will be proportional to the distance between ram 354 and theinner end 360 of screw 359.

These events take place well before the main engine pistons 104L and104R are released, because pressure in the space 346 will not fallsufficiently to allow the high-pressure reservoir pressure, acting onthe spool valve 309, to overcome the force exerted on ram 328, until thepiston 353 has completed its stroke, and also because the effectiveratio of force to mass, acting on the spool valve 309, is considerablyless than the corresponding figure for the piston 353; the distance thatmust be traversed by the spool valve 308 before any action takes placeis therefore considerably greater than is the case with the piston 353.

RUNNING THE POWER UNIT

Until the tip of the operating rod 304 touches the transmission rod 305,the quantity of fuel injected into the cylinder in each cycle issufficient to keep the engine running, but is not sufficient to closethe valve 610. When, however, the operating rod 304 is advancedsufficiently to move the transmission rod, this action increases thefuel injected into the cylinder so that pressure and flow increasesufficiently in the manifold 569 to close the bypass valve 610, and thusmake oil available for traction.

OPERATION -- STOPPING THE ENGINE

The engine may be stopped simply by removing all pressure from theoperating rod 304. A spring (not shown) then pulls it down. When thistakes place, the reversed L surface on the rod 304 catches theprojection on the slide 306 and pulls the latter up. This releases thespool valve 308, which is then pushed down by pressure from thepressurized oil sump, 68 (supplemented if necessary by a spring) andhigh pressure oil from the outlet 318 acts upon ram 328 which thenforces the spool valve 309 in an upward direction. The spool valve 309however is not able to move until the average pressure in the oil pipe515 falls to the value that appertains when the engine is idling. Untilthis low value is reached, the spool valve 356 of device 57 (FIG. 41)remains up. The pressures acting in oilway 340, oil entrance 314, andagainst bolt 329 (FIG. 27) therefore remain steady and too high to allowthe ram 328 to force it out of the groove 332.

When the average pressure in the pipe 515 falls to the correct value,however, the spool valve 356 descends to the position shown in FIG. 41and is therefore open to the pulsating oil pressure that is transmittedthrough pipes 515 and 551 from the pump chambers 112 (FIG. 1).

Pressure in the pump chambers 112 falls to zero momentarily during thecompression stroke of the engine pistons, when re-compressionaccumulator pistons 123 are brought to rest at the end of their stroke.This pressure drop is transmitted through the large area passages of thetubes 515 and 551, valve 57 and tube 363, to piston 330 of FIG. 27. Thepressure already being exerted on the ram 328 is then able to force thespool valve 309 up, while displacing the bolt 329 from the groove 332.Pressure on the piston 330 is soon re-asserted, but by this time thebolt 329 is out of the groove; and the design is such that the force ofthe bolt is neither sufficient to prevent the piston 309 from moving,nor to damage the sliding surfaces. Once released from the bolt 329, thepiston 309 moves out under the force exerted by the ram 328 (minus thevarious frictional losses), with its speed controlled by the orifice331.

By correct apportioning of the relevant dimensions these means make itpossible to advance the plungers 170 (FIG. 1), at about the same timethat the grooves 169 in the engine pistons are ready to receive them,near the end of the expansion stroke. An orifice 167 limits the entryspeed of the plungers 170 to such a value that they do not significantlyaffect the speed of the engine pistons as they slide down the edges ofthe grooves 169. The design is such as to bypass the orifice 167 whenthe plungers 170 release the engine pistons.

Under some conditions it may be preferable not to employ a gas-turbineto run the compressor which boosts the inlet air pressure to the engine,but to do it by other means. For example, one may use the pressurizedliquid output of the engine to power a compressor. In this case theexhaust intake tube 158 (FIG. 1) may be used to operate a hydraulicvalve instead of the spool valve 160; this valve would then open orclose a supply of oil from any suitable part of the hydraulic system asrequired.

All the features described in the foregoing specification would notnecessarily be simultaneously employed. For example: the four drivemotors could be replaced by a single hydraulic motor delivering power tothe differential gear of a present-day automobile, and the brake systemdescribed could be modified or omitted. Furthermore, although aparticular application of the invention has been described, it is to beunderstood that power units in accordance with the invention havenumerous applications. In general, a power unit in accordance with theinvention is used to provide a supply of pressurized hydraulic fluid fordriving hydraulic machinery; such a unit may be used, for example, todrive a ship's propellor, an electric generator, a hoist, or a largeextrusion press.

What I claim as my invention is:
 1. A hydraulic power transmissionsystem comprising:first and second drive units each including one ormore hydraulic motors; conduit means connected to the motors forsupplying working fluid thereto, said conduit means further including acommon return pipe connected to the motors for returning fluidtherefrom; a two-position valve in circuit with the motors of one saiddrive unit, the motors of the other drive unit being suppliedindependently of said two-position valve, said valve having a firstoperative position for blocking flow of working fluid to said one driveunit and a second operative position for permitting flow of workingfluid to said one drive unit, said valve being operable between itsfirst and second positions for selective operation of one or both driveunits; a spring-loaded valve in circuit with the return pipe, thespring-loaded valve being displaceable from an open to a closed positionto restrict fluid flow along the return pipe and so effect braking ofthe motors; and a pressure-responsive valve means responsive to pressurein the return pipe for effecting displacement of the two-position valveto the second operative position when said pressure exceeds apredetermined value.
 2. A hydraulic power transmission system accordingto claim 1, wherein the two-position valve is a spool valvespringbiassed towards its first position, the spool valve beingdisplaceable to its second position by a hydraulic ram operating in achamber to which pressurized fluid is supplied, the system furtherincluding selector means for selectively controlling the supply of thepressurized fluid to said chamber.
 3. A hydraulic power transmissionsystem according to claim 2, wherein the selector means includes asolenoid-operated spool valve having an inoperative position forblocking flow of fluid to said chamber, and an operative position foradmitting pressurized fluid to said chamber whereby to displace thetwo-position valve from its first position to its second position.
 4. Ahydraulic power transmission system according to claim 3, wherein thesolenoid-operated spool valve is connected to a further spool valve by alost-motion connection, the further spool valve being responsive to flowof working fluid and operable to hold the solenoid-operated spool valvein its inoperative position when the velocity of flow of working fluidexceeds a predetermined value.
 5. A hydraulic power transmission systemaccording to claim 2, said selector means including an automaticspring-loaded valve having a closed position for blocking flow of fluidto said chamber and an open position for admitting pressurized fluid tosaid chamber whereby to displace the two-position valve from its firstposition to its second position, the automatic valve being responsive topressure of working fluid and being displaceable to its open position inresponse to the working fluid pressure exceeding a predetermined value.6. A hydraulic power transmission system according to claim 1, includinga pressure control valve positioned in said conduit means formaintaining the pressure of working fluid, and a pressure-responsivevalve operatively connected to said pressure control valve and operablein response to pressure of working fluid in the return pipe forrendering the pressure control valve inoperative during braking.
 7. Ahydraulic power transmission system according to claim 1, wherein saidconduit means includes a reversing valve for reversing the flow ofworking fluid through said motors, a mechanical interlock between thereversing valve and said spring-loaded valve to prevent actuation of thereversing valve save when the spring-loaded valve is fully closed, andmeans responsive to working fluid pressure in the return pipe to preventfull closing of the spring-loaded valve when said working fluid pressureis greater than a predetermined value.
 8. A hydraulic power transmissionsystem according to claim 1, including means responsive to fluidpressure in the return pipe for maintaining the two-position valve inits second position when the fluid flow through the motors is reversed.